The present invention relates to a multi-piece solid golf ball. More particularly, it relates to a multi-piece solid golf ball which has excellent flight performance by accomplishing high launch angle and low spin amount when hit by a driver or a long iron club or a middle iron club; has good controllability by accomplishing high spin amount when hit by a short iron club or approach-shot; has light and good shot feel by accomplishing good rebound characteristics when hit by a driver or a long iron club or a middle iron club; and has good controllability by accomplishing large contact area of the ball with a club face and light and good shot feel when hit by a short iron club or approach-shot.
Amateur golfers generally regard flight distance as most important factor for golf balls and use a golf ball having good rebound characteristics and little spin amount, such as a solid golf ball, by choice. On the other hand, professional golfers and high level-amateur golfers generally regard controllability as most important factor for golf balls, and regard soft and good shot feel and flight performance as the next important factor for golf balls. Therefore they have mainly used thread wound golf balls, which have good controllability and soft and good shot feel. However, since the thread wound golf ball has a structure easily putting spin thereon, there has been a problem that the spin amount is large when hit by any type of golf club, which reduces the flight distance. In order to solve the problem, many solid golf balls having good shot feel and excellent flight performance while maintaining good controllability have been proposed in Japanese Patent Kokai Publication Nos. 239067/1997, 332247/1996, 313643/1997 and the like.
Japanese Patent Kokai Publication No. 239067/1997 suggests a two-piece solid golf ball comprising a core and a cover. The core has a surface hardness in JIS-C hardness of not more than 85, a center hardness of the core is lower than the surface hardness of the core by 8 to less than 20. A hardness of from the surface to 5 mm from the surface of the core is lower than a surface hardness of the core by not more than 8. A hardness of the cover is higher than the surface hardness of the core by 1 to 15. A thickness of the cover is 1.5 to 1.95 mm, and a number of dimples is 360 to 450.
Japanese Patent Kokai Publication No. 332247/1996 suggests a three-piece solid golf ball comprising a core having a two-layer structure of an inner core and outer core, and a cover. The inner core has a diameter of 25 to 37 mm, a center hardness in JIS-C hardness of 60 to 85 and a hardness difference in JIS-C hardness between the center point and surface of the inner core of not more than 4, the outer core has a surface hardness in JIS-C hardness of 75 to 90, and the cover has a flexural modulus of 1,200 to 3,600 kg/cm2.
Japanese Patent Kokai Publication No. 313643/1997 suggests a three-piece solid golf ball that an intermediate layer is placed between a core and a cover. The core has a center hardness in JIS-C hardness of not more than 75, a surface hardness in JIS-C hardness of not more than 85, the surface hardness is higher than the center hardness by 5 to 25, a hardness of the intermediate layer is higher than the surface hardness of the core by less than 10, and a hardness of the cover is higher than that of the intermediate layer.
In the golf balls of the above publications, the flight performance when hit by a driver is improved, but the spin amount is large, which reduces flight distance, when hit by a long iron club or middle iron club still in need of long flight distance. In addition, the shot feel of the golf balls is hard or heavy in order to improve the flight distance, and good shot feel is not sufficiently obtained.
A main object of the present invention is to provide a multi-piece solid golf ball having excellent flight performance, good controllability and good shot feel.
According to the present invention, the object described above has been accomplished by providing a multi-piece solid golf ball comprising a core composed of an inner layer core and an outer layer core and at least one layer of a cover formed on the core, and adjusting a diameter and center hardness of the inner layer core, a thickness and surface hardness of the outer layer core, a hardness distribution of the core, and a thickness and hardness of the cover to specified ranges, thereby providing a multi-piece solid golf ball having excellent flight performance, good controllability and good shot feel.
This object as well as other objects and advantages of the present invention will become apparent to those skilled in the art from the following description with reference to the accompanying drawings.